Ontogeny of Hemopoietic Colony-Forming Units in the Chick Embryo Spleen

Summary

Inoculation of spleen cells of chicken embryos onto the chorioallantoic membrane (CAM) of other chicken embryos led to the formation of white (granulocytic) and pink (mixed erythrocytic and granulocytic) hemopoietic colonies. The number of CAM colonies formed was a linear function of the number of cells inoculated indicating that each colony originated from a single colony-forming unit (CAM-CFU). CAM-CFU’s consist of an aggregate of primitive undifferentiated cells which penetrate the ectodermal layer of the CAM, then proliferate and differentiate into mature granulocytes or erythrocytes. Deaggregated CAM-CFU’s failed to form colonies indicating that cell interaction may be required for colony formation. The genetic constitution of the host embryo has no effect on colony formation but mixtures of donor cells from inbred embryo spleen were found to be more efficient colony formers than mixtures of donor cells from non-inbred embryo spleens. Ontogeny studies demonstrated that the chick embryo spleen contains peak hemopoietic activity between fifteen and seventeen days of incubation declining thereafter to undetectable levels two days post hatching. At this time the inoculation of spleen cell suspensions leads to the formation of lymphoid colonies which increase in number with age of the donor.